A strong correlation between \(\Gamma \)  and \(\nu _{QPO}\)  has already been observed in a number of X-ray binaries, for example 4U 1608\(-\) 52 and 4U 0614\(+\) 091 [1]}, XTE J1550\(-\) 564 and GRO J1655\(-\) 40 [2]}, Cyg X-1 [3]} and Cyg X-2 [4]}. [2]} observed a positive correlation for XTE J1550\(-\) 564 and a negative correlation for GRO J1655\(-\) 40. The authors explained that an increase in the mass accretion rate increases the QPO frequency, and the contribution from the power-law should be more than 20 % for QPOs to be present. [2]} have also suggested that the opposite correlation in XTE J1550\(-\) 564 and GRO J1655\(-\) 40 could be due to different regions of QPO generation in the two sources. To explain the correlations, [7]} proposed the transition layer (TL) model. According to this model, a compact bounded coronal region is formed as a natural consequence of the adjustment of the Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central region. It ultimately ends up forming a TL between the adjustment radius and the innermost boundary. However, this mechanism is unable to produce the inclination-dependent QPOs obtained by [8]}.
